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An overview of current theories of planetary
formation, with emphasis on giantplanets, is presented.
The most detailed models are based upon observations
ofour own Solar System and of young stars and their
environments. While these models predict that rocky
planets should form around most single stars, the
frequency of formation of gas giant planets is more
difficult to predict theoretically. Terrestrial planets
are believed to grow via pairwise accretion until the
spacing of planetary orbits becomes large enough that the
configuration is stable for the age of the system. Giant
planets begin their growth as do terrestrial planets, but
they become massive enough that they are able to
accumulate substantial amounts of gas before the
protoplanetary diskdissipates. Most models for extrasolar
giant planets suggest that they formed as did Jupiter and
Saturn (in nearly circular orbits, far enough from the
star that ice could), and subsequently migrated to their
current positions, although some models suggest in situ
formation.
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